A pliable cover for an upwardly open truck body, cargo container, or trailer serves both to protect a load within the body, container, or trailer and to minimize the likelihood of all or part of the load from escaping therefrom. Because covers of this type are often large and unwieldy, some form of mechanical assistance is required to spread and secure the cover. Truck cover manipulators provide this assistance.
Spreading a cover across a trailer or container over 30 feet in length presents particular challenges. One approach to covering very long trailers is a cable or track type system, wherein a cover is pulled horizontally over the trailer. Cable or track systems generally include movable elements attached to a cover and which are engaged with tracks or guides associated with the sides of the trailer. Deformation of the sides of a trailer, however, can displace the tracks of a cable or track type system, thereby causing the movable elements to bind and thus preclude normal extension and retraction of the cover. Trailers used for transporting rubbish, for example, are generally 40 to 50 feet long and develop outwardly deformed or bowed sides.
Another drawback of cable or track type systems is that in order to extend and retract the cover, the load cannot be heaped up above the plane of movement of the cover during deployment. This requires that the trailer be either under-filled or that the contents be carefully leveled after loading. If it were not for this limitation, certain materials (depending on the particular characteristics of the material to be transported) could be heaped up significantly without exceeding the weight limitation of a given trailer.
Another approach to covering an upwardly open container is represented by pivot arm systems, wherein two parallel arms are pivotally engaged on opposite sides of a trailer and move in unison to draw a cover from one end of the trailer to the other. However, if a system having non-telescoping arms is used in association with a long trailer, the arms have such a length that the cover is raised into the air like a sail during deployment and retraction. If even the slightest breeze is present, the arms and cover can be subjected to a load so high that the system ceases to function or is damaged. Additionally, the great length of the arms requires significant overhead clearance. Particular care is required when operating in the vicinity of power lines, as contact between the lines and the arms could prove fatal to the system operator.